There are a myriad number of applications in which an integrated circuit (IC) requires a reference signal generator. These applications encompass both digital devices and analog devices. Reference signal generators typically supply clock signals that drive a processing circuit at a desired (or target) speed (or frequency). Often, one or more of the signal parameters (i.e., frequency, amplitude, duty cycle) of the reference signal is adjustable.
One important signal parameter is duty cycle. The duty cycle of a reference signal is the percentage of one cycle (or period) of the reference signal when the reference signal is high (or Logic 1). For example, a 200 KHz reference signal has a T=5 microsecond period. If the 200 KHz reference signal is high (e.g., Logic 1) for 2 microseconds and low (e.g., Logic 0) for 3 microseconds, the 200 KHz reference signal has a ⅖=40% duty signal. Similarly, if the 200 KHz reference signal is high for 2.5 microseconds and low for 2.5 microseconds, the 200 KHz reference signal has a 50% duty signal (i.e., a square wave).
However, many applications require high precision and operate under extreme temperature conditions. One typical example is a cell phone, which typically includes high-precision components and may operate in temperatures from sub-zero to 100+ degree. For these types of applications, a conventional reference signal generator may experience significant variations in the duty cycle of the reference signal across such a wide range of operating conditions.
Therefore, there is a need in the art for reference signal generators that generate reference signals having variable duty cycles. In particular, there is a need for reference signal generators that produce highly accurate duty cycles across a wide range of operating conditions.